You can use an ammonia removing filter pad. I currently use a pad that removes ammonia and ammonia doesnt register and hasn't since the day after I started using it.
I hate advertising, but petmountain has a great black Friday sale going on until the 25th. Four days to pick up what you need or want.
Trace $4.41 (250 ml)
Potassium $4.47 (250 ml)
Carbon/Krebs $4.47 (8.5 oz)
Ammonia pad (18x10) $4.48
Phosphate Pad (18x10) $4.73
Carbon Pad (18x10) $4.16
Total $26.72 (free shipping @ $25.00) code: black25
Yellowstone National Park: 12-28-2012 to 1-3-2013
March Madness, Rio, Las Vegas 3-20-2013 to 3-26-2013
Glacier National Park or Vegas, September 2013???